Circuits for relaying or amplifying direct or alternating current energy



April 3, 1934.

CIRCUITS FOR RELAYING 0R AMPLIFYING DIRECT 0R ALTERNATING CURRENT ENERGYFiled Sept. 19, 1931 'Ezj I I I MI I I P h'wventof': Evnest Y Robinson,

by Maw.

His Atcovneg.

E. Y. ROBINSON 1,953,775

Patented Apr. 3, 1934 UNITED STATES PATENT OFFICE ENERGY Ernest YeomanRobinson, Enfield, England, assignor to General Electric Company, acorporation of New York Application September 19, 1931, Serial No.563,834 In Great Britain September 29, 1930 5 Claims. (Cl. 179-171) Thisinvention relates to circuits for relaying or amplifying direct oralternating current energy by means of vacuum tube devices. In the caseof alternating current, the invention relates especially, but notexclusively, to circuits designed to give a periodic amplification, thatis, amplification which is independent of the frequency of the appliedsignal and which circuits can be employed for the amplification ofslowly 10 varying potentials ifdesired.

The invention also relates to means whereby the control grid of a vacuumelectric tube may be operated at a highly positive potential evengreater than that of the anode.

It is ordinarily necessary for the control grids of vacuum tubes to beoperated at a negative potential with respect to the cathode. They mayin some cases be operated at a slight positive potential but in anyevent at a potential which does not approach that of the anode, with theresult that when two or more tubes are operated in cascade. it isnecessary to use inductive or capacitative coupling from the anode ofone device to the grid of the succeeding device, or alternatively toprovide biasing means between one tube and the next, either by a biasbattery, for example, between the anode of one tube and the grid of thenext, or by a bias battery between the cathode of one tube and thecathode of the succeeding tube. Circuits employing capacitative orinductive coupling means are not suitable for the amplification ofslowly varying signals or of direct current, while circuits employingbiasing means are difficult to adjust and maintain in adi justment.

According to the present invention the improved tube comprises acathode, a control grid to which the signal to be amplified is applied,an anode and an additional grid disposed between said coni trol grid andthe anode, said additional grid being connected to a fixed source ofpotential, preferablyzero or negative. Preferably such additional gridis connected to the cathode.

In one known tube construction three grids are interposed between thecathode and the amide, and the grid adjacent to the anode is connectedto the cathode. In certain applications of the present invention, a tubeof this known type may be employed, in which case the intermediate gridis employed as the control grid and the grid adjacent to the cathode maybe employed for other purposes, for example, as a space charge grid oras an additional grid for detection of modulated radio frequencysignals.

The invention also comprises an amplifying circuit of the kind specifiedcomprising two or more cascade coupled thermionic devices in which theoutput circuit of one tube is in direct electrical connection with thecontrol grid of the succeedr' ing tube wherein a further grid isdisposed between said control grid and the anode and connected to asource of low or zero or negative potential and preferably to thecathode. In such a circuit, a resistance may be provided in the anodecircuit of the output tube with a connection therefrom to the controlgrid of the preceding tube for providing regeneration.

The invention also comprises an amplifying circuit of the kind specifiedhaving two tubes arranged in push-pull relation, wherein each tubecontains at least two grids of which the grid adjacent the anode isconnected to a source of low or zero or negative potential, While meansare provided for supplying the grids adjacent the first-mentioned gridswith positive potential and a varying potential having a phase oppositeto that of the respective anodes and preferably equal to each other soas to provide regeneration. Said varying potentials may be obtained fromthe potential drops across a resistance. In this circuit tubescontaining five electrodes may be employed and the input or signalvoltage may be applied to the grid of one tube which grid is adjacentthe cathode or the signal may be bisected and applied to the gridsadjacent the respective cathodes of both tubes. The circuit just aboveset forth may embody means for applying a modulated radio-frequency tothe grids and means for demodulating said frequency. H

To enable the invention to be clearly understood it will now bedescribed with reference to the accompanying drawing, the figures ofwhich show amplifying circuits embodying the present invention.

In one application of the invention as shown in Fig. 1, two 4-electrodetubes 15 and 16 are employed, the outer grids of which are connected tothe cathodes as hereinbefore described and the coupling impedancesconsist of anode resistances 17 and 18. Regeneration or feed-back isintroduced by connecting the grid of the first tube 15 to a tap 19 onthe anode resistance of the second tube 16. As the tap is moved nearerto the anode of the second tube, the regeneration and amplification maybe increased until the system becomes unstable. When regeneration is sogreat as to cause instability, the circuit may be employed as a negativeresistance device for producing oscillations or for compensating for theresistance in other circuits coupled thereto. When the circuit isemployed as a negative resistance device, the negative resistance effectis obtained across the terminals 20. The circuit may be employed in avariety of ways. For example, a tuned circuit comprising a condenser andinductance in parallel may be connected across the terminal points justmentioned whereby oscillation will be generated in said tuned circuit.When the device is to be used as an amplifier the signals to beamplified may be applied to the terminal points and theresultingamplified signals taken from the terminals 21. A disadvantage of thearrangement just described is that the device has a low inputresistance. This may be overcome by using 5-electrode (pentode) tubesemployed as shown inFig. ,2.

The anodes of the two tubes 22 and 23 are connected to the extremitiesof a centre tapped resistance 2d, the centre point of this resistancebeing joined to the cathode through a battery or other high tensionsource 25. The intermediate grids of the tubes are connected to sliders26 and 27 which are preferably adjusted to be equidistant from thecentre tap of the aforesaid resistance. Such taps provide regenerationin the circuit and as they are moved away from the centre theregeneration in the circuit is increased until instability ensues. Theapplied signals may be introduced across the two innermost grids 23 and29 of the two tubes by means of a centre tapped impedance such as thetransformer secondary 30 connected to such grids and to the cathodes.When it is inconvenient to connect a centre tapped impedance across thegrids as above described, as for example, when the impedance isresistive and the circuit is employed for amplifying slowly varyingsignals, the signals may be applied between the innermost grid 29 or"one of the tubes and the cathode. In this case, the innermost grid 28 ofthe other tube can either be connected to the cathode or to the negativeterminal of any biasing battery employed at 31 between the impedanceconnected between said input grid and the cathode.

In a further example shown in Fig. 3, using tw S-electrode tubes inwhich the circuit is used for the detection and amplification ofmodulated radio frequency signals, the anodes of the tubes 33 and 34 areconnected to the extremities of the primary winding 32 of an outputtransformer, the winding 32 having a centre tap connected to the cathodethrough the high tension source 35 while the secondary winding of suchtransformer may be connected to a loud speaker. A resistance 36 is alsoconnected across the two anodes and the two intermediate grids of thetubes are connected to taps on this resistance, equally spaced from theelectrical centre but on opposite sides. Radio frequency signals arereceived in a tuned circuit 3'? one end of which is connected to thecathodes and the other through a condenser 38 and a leak resistance 39to the grid adjacent to the cathode of the tube 33, thus providing anarrangement which gives cumulative grid detection. The grid adjacent tothe iathode oi the other tube 34 is connected to the cathode. Whenanode-bend detection is used the return lead from the tuned circuit 37is connected to a negative bias battery in which case the grid adjacentto the cathode of the other tube is connected to the same bias toprovide symmetry. In order to provide as much regeneration as possiblewithout producing an audio frequency resonance or without producinginstability, the loud speaker should be so chosen that as far aspossible the load is resistive. It is obvious that the resistance 36 maybe dispensed with and the intermediate grids of the two tubes beconnected to equally spaced taps on the centre tapped primary 32 of theoutput transformer.

In i-electrode tubes improved in accordance with this invention the gridadjacent to the anode may be connected to a negative potential ifdesired, but in the preferred method it is connected to the cathode bymeans of a connection inside the envelope or inside the cap of the tube.

It is obvious that two or more complete sets of electrodes with orwithout the coupling resistances may be mounted within one envelope, andthis invention facilitates the manufacture of such multi-stage tubessince the necessity for coupling condensers between the anode of oneelectrode system and the grid of a succeeding electrode system iseliminated.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. An amplifying system comprising a plurality of coupled amplifiers,each containing an anode, a cathode, and a control member, the couplingconsisting of an equipotential conductor connected between the anode ofone tube and the control member of a succeeding tube, and means forenergizing the system, said means comprising a source of electrornotiveforce connected to each of the anodes respectively through resistances,and a connection between one of said resistances and the control memberof a preceding amplifier.

2. An amplifying system comprising a plurality of coupled amplifiers,each of which includes a cathode, an anode, a control grid and a secondgrid interposed between the control grid and the anode and connected tothe said cathode, the. coupling between amplifiers consisting of anequipotential conductor connected between the anode of one amplifier andthe control member of the succeeding amplifier, said amplifiers beingenergized by a common source of electromotive force through resistancesconnected respec-. tively to each of the anodes, and a connectionbetween one of said resistances and the control grid of a precedingamplifier.

3. An amplifying system comprising a plurality of thermionic devicesarranged in push-pull relation, each of said devices including a oath--ode, an anode, a control grid, and two grids between the control gridand the anode, thegrid nearest the anode being connected directly to thecathode, means for energizing the system and for supplying the gridadjacent to the control grid with positive potential and also with avarying potential having a phase opposite to that of its respectiveanode whereby regeneration is produced in the system.

4. An amplifying system comprising a pair of thermionic devices, each ofsaid devices including a cathode, an anode, a control grid and two gridsbetween the control grid and the anode, the grid nearest the anode inboth tubes being connected directly to the respective cathodes, thecontrol grid of one of said tubes being also congrid nearest the anodein both tubes being connected directly to the respective cathodes, thecontrol grid of one of said tubes being also connected to the cathode,means for energizing the system, and a connection between the anode ofone tube and the grid adjacent the control grid of the other tube, saidconnection including an impedance.

ERNEST YEOMAN ROBINSON.

